Letter abstract
Nature Cell Biology 8, 407 - 415 (2006)
Published online: 12 March 2006 | doi:10.1038/ncb1383
Evidence for the existence of an HP1-mediated subcode within the histone code
Gwen Lomberk1, Debora Bensi1, Martín E. Fernandez-Zapico1 & Raul Urrutia1
Currently, the mammalian heterochromatic proteins HP1
, HP1
and the pan-nuclear HP1
are considered 'gatekeepers' of methyl-K9-H3-mediated silencing. Understanding how the binding of these proteins to post-translationally modified histones is switched on and off will further our knowledge of how the histone code is modulated. Here, we report that all three HP1 isoforms can be extensively modified, similar to histones, suggesting that the silencing of gene expression may be further regulated beyond the histone code. To assess the potential impact of these modifications, we analysed the phosphorylation of HP1 at Ser 83 as a 'model modification'. We demonstrate that P-Ser 83-HP1 has an exclusively euchromatic localization, interacts with Ku70 (a regulatory protein involved in multiple nuclear procesess), has impaired silencing activity and serves as a marker for transcription elongation. These observations predict that regulation of silencing by methyl-K9-H3 through modification of mammalian HP1 proteins may be more complex than previously thought and suggests the existence of an HP1-mediated 'silencing subcode' that underlies the instructions of the histone code.
- Gastroenterology Research Unit, Department of Medicine, and Mayo Clinic Cancer Center, Rochester, MN 55605, USA.
Correspondence to: Raul Urrutia1 e-mail: urrutia.raul@mayo.edu
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